The present invention relates to a method and apparatus for measuring pressure, sound or vibration, especially with regard to analyzing fluid flow on missiles, as well as to a method of analyzing the flow on surfaces of structural parts of missiles and in the field of aviation.
The characterization of fluid flows on surfaces of structural parts has become increasingly important in various fields of technology. Particularly for airplane wings, knowledge of the flow characteristics permits optimization of the wing shape for particular usage conditions. As a result, flying characteristics can be improved, and fuel requirements reduced.
In addition, in other fields of technology, fluidic measuring methods are required in order to improve aerodynamics. For example, in automotive engineering, fuel consumption can be reduced by optimizing the shapes of structural parts, for example, in the area of the intake train.
In order to measure flow characteristics at wings of airplanes, piezoelectric pressure foils and membrane pressure sensors have been mounted on the wing surface, for example in the lab or in a wind tunnel. The article xe2x80x9cShock Detection by Means of Piezofoilsxe2x80x9d, W. Nitsche et al., Zeitschrift fxc3xcr Flugwissenschaften und Weltraumforschung 15(1991), Pages 223-226, Springer Publishers, discloses a measuring method for detecting compression shocks on flow bodies. In this case, a sensor array, in the form of a thin piezoelectric foil, is mounted on the body to be tested, and used to detect the unsteady fluctuations of pressure, shearing stress and temperature and thereby supply information on the position of compression shocks.
The piezofoil is mounted on a wing, and the flow-induced local pressure fluctuations are measured. As a result, characteristic RMS values are determined by way of the wing profile in order to determine the position of the compression shock or the shock position. However, known systems of this type have the disadvantage that the sensors are exposed to high stress, particularly due to the effects of dirt and ice, which may impair the measuring results, and even destroy the sensors. Furthermore, as a result of an interaction with the flowing medium, the sensors change the original flow and therefore corrupt the measuring results. As an additional fact, high-expenditure production and maintenance work is required. The sensors glued onto the component surface are therefore susceptible to various types of damage (for example, because of dirt, impact of birds, etc.), and require high expenditures for production and maintenance.
It is therefore an object of the present invention to provide a device for measuring pressure, sound and/or vibration which is robust and cost-effective.
Another object of the invention is to provide such a measurement device which is suitable for an operational usage or for a series, and supplies the exact measuring result while the service life is long.
Furthermore, still another object of the invention is to provide a method of analyzing the flow on surfaces of structural parts which is particularly suitable for applications in aviation.
Finally, yet another object of the invention is to provide such a method by means of which, in operational usage, the flow characteristics can be determined on the structure of a structural part.
These and other objects and advantages are achieved by the method and apparatus according to the invention for measuring pressure, sound and/or vibration, which comprises a sensor device for sensing pressure waves or sound waves which is linked to a structure of a part in order to measure forces acting upon the surface of the structural part. The sensor device is arranged completely within the structure of the part or on the rear side of the surface of the structural part, so that the device is protected against damage also under extreme stress, as, for example, when used on the wings of airplanes, and the service life is increased.
Advantageously, the device also comprises a unit for analyzing signals by means of artificial intelligence methods, so that it is possible to determine with high accuracy the flow characteristics, based on measured values detected below the surface of the structure of the part. The sensor device preferably comprises a plurality of pressure sensors which are arranged below or on the rear side of a shell of the structure of the part. The sensor device may, for example, be a piezoelectric foil which is fixedly connected with the interior side of the outer wall of the structure of the part. In particular, the structure of the structural part may be a wing of a missile, in which case the sensor device is arranged, for example, below the wing shell in a wing area.
Data lines and/or supply lines of the sensor device may be arranged or integrated completely in the structure of the part. In this manner, the lines can have no influence on the actual flow, so that more precise measuring results can be achieved. In addition, the reliability of the measured value detection is increased because the lines are protected from damage.
The device is advantageously designed such that frequencies of 250 KHz or less are used to characterize the flow on the surface of the structural part, particularly for detecting the start of turbulence, the position of a compression jolt, buffeting, and/or local surface friction. Thus, local flow characteristics can also be detected with high precision by the surface material, in which case lateral disturbances are suppressed by exponentially decreasing structure-borne noise in the structure material.
Metals or plastic materials, such as aluminum, steel or CFK are preferably used as surface material. When the thickness of the material is no greater than 5 mm, no special electronic amplifiers are required in order to receive signals suitable for the processing.
Advantageously, the device is a sensor module which is further developed as a component of the structure of the structural part. As a result of the modular installation without any modification of the surface exposed to the flowing medium, a cost-effective production is achieved and the maintenance possibilities are improved.
The device can also be utilized advantageously in a space segment whose temperature can be adjusted, or which can be heated or cooled and which can, for example, be insulated. As a result, a reliable and durable detection of the measured values without any failures can also be achieved at very low outside temperatures, for example, at xe2x88x9250xc2x0 C. at an altitude of 10 km. The measuring module itself as well as mechanical interfaces (for example, adhesive substances) are protected in this manner from damage by material fatigue because of temperature fluctuations.
The method according to the invention for analyzing the flow on surfaces of structural parts is particularly suitable for applications in aviation. In this case, pressure, sound and/or vibrations are measured at an inside surface of the structure of a part, and artificial intelligence is used to determine at least one of the parameters turbulence start, compression shock, buffeting, and local surface friction. As a result of the special analyzing method by means of artificial intelligence, all information of the measured data series are used, including a supposed noise, in order to determine the flow characteristics. In this manner, increased precision is achieved without requiring preprocessing steps for eliminating systemic disturbances.
The method according to the invention also comprises filtering processes for the preprocessing of signals, for the extraction of characteristics, and/or classification methods.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.